Interpretive Summary: Irrigated agriculture will be forced to relinquish part of its water supply with the increased demand for water to meet municipal and industrial needs. This will be at a time when there is a need to increase the food supply by 1 to 2% a year and irrigated agriculture will have significant role to play. These conflicting goals can be met by improving the water use efficiency of irrigated agriculture. This means that crop production is more efficient or more crop per drop. This can be done by improving irrigation management and efficiency, by improving fertilization, and managing ground water. Data presented show that yields of pears were maintained using 33% less water by using regulated deficit irrigation. This a technique to provide the crop water demand during critical periods and withhold at other times. Fertilization with nitrogen, phosphorus, and potassium using drip irrigation resulted in a 70% increase in water use efficiency. Implementing high frequency irrigation to minimize plant stress resulted in a 20% increase in water use efficiency in tomato. Managing a subsurface drainage system to enable crops to use shallow ground water is another technique to improve irrigation water management. Field crops, such as cotton and alfalfa, have taken nearly 50% of their water requirement from shallow ground water resulting in less water demand. There are many proven ways to improve irrigation and water use efficiency, the problem is implement them.

Technical Abstract:
Increasing demand for food, fiber, and clean water resulting from the increase in world population is putting significant stress on irrigated agriculture. Currently, irrigated agriculture supplies nearly 40% of the world food products and is expected to contribute more in the future with less water and the same cultivated land area. Analysis of the global water supply and existing irrigation management reveals many alternatives for irrigated agriculture to meet the production challenges with the same water supply while minimizing the environmental impact of irrigated agriculture. These alternatives include: improving existing water management practices for surface irrigation, switching to alternative irrigation systems, improved management to include fertilizer management and the use of alternative water supplies including saline drainage water and treated effluent. In addition to water application, sustaining irrigated agriculture depends on managing the salt in the soil profile and the salt load emanating from the irrigated area. This can be accomplished by improving drainage system management and changing the drainage design criteria. Data from the U.S. and Australia are used to demonstrate the effect of changes in irrigation system management on water use efficiency and drainage system design and management on the salt load from irrigated agriculture.